1. Field of the Invention
The present invention relates to the field of dyeing cationic polyamide fiber, and the dyed cationic polyamide fiber resulting therefrom.
2. Prior Art
Dyeing techniques for the dyeing of cationic dyeable polyamide fiber, such as cationic nylon carpet fibers, with acid or premetalized acid dyes are well-known in the art. Known dyeing techniques include traditional batch dyeing (also referred to as beck or winch dyeing) wherein a complete textile substrate is dyed to a uniform color by placing a finite amount of the substrate into a dyeing machine for a given length of time, and running the substrate through a batchwise cycle during which time the substrate is usually immersed in an aqueous bath which contains the dyes and other necessary chemicals. The bath is heated for a length of time sufficient to exhaust the dye onto the substrate. Thereafter, the dye bath is drained, and the dyed substrate rinsed and then removed from the dye bath to a dryer.
Another known dyeing technique is space dyeing. Space dyeing is the dyeing of multiple colors along a single length of yarn. The dye colors selected for use in space dyeing are usually intense, saturated colors (deep shades), selected for their desired visual effect. The resulting space dyed fibers are especially popular in carpet manufacture.
Similarly, a dyeing technique referred to as printing is known for selectively placing one or more colors of dye on or in a textile substrate in a predetermined pattern. Printing may be accomplished using, for example, the following printing machines which are well known in the art: Tak, Foamcolor, Polychromatic (flow printers); Zimmer & Mitter (screen printer); Millitron, Titan, Chromatronic (jet printers).
Additionally, techniques are known for continuous dyeing of a textile substrate. Rather than placing the substrate in a dye bath, as is done in the batch dyeing technique, the dye is applied to the material by, for example, feeding the substrate in one end of a machine and applying the dye liquor. The substrate continues into a fixation chamber, usually a steamer, where it passes through steam for a sufficient amount of time to allow the dye to fix onto the substrate. Thereafter, any loose dye and chemicals are rinsed from the substrate and the substrate is dried.
Two important factors relative to the particular dyeing technique utilized are strike rate and exhaustion. The term "strike rate" refers to length of time necessary to fix the dye to the substrate being dyed. The term "exhaustion" refers to how completely a dye fixes to the substrate being dyed.
When the batch dyeing technique is used, the strike rate must be slow enough to result in a controlled, even dyeing of the substrate. If the strike rate is too fast, uneven dyeing of the substrate can result. After a slow, even strike has been achieved, if necessary, the dye can be exhausted by, for example, lowering the pH of the dye solution. See U.S. Pat. No. 5,164,261 issued to Windley on Nov. 17, 1992.
In contrast, when space dyeing or printing techniques are used to dye a substrate, the strike rate must be fast, i.e. 30-90 seconds, and dye exhaustion complete. If a fast strike rate is not achieved, the different colored dye liquors which adjoin at the color change interfaces will come in contact with one another and smear. Additionally, unacceptable color transfer can occur if the dyed substrate is plaited during fixation (such as steaming). If exhaustion is poor, the dyed substrate demonstrates low color yield and a large amount of unfixed dye remains in the waste water which must then be treated before disposal of the waste water.
U.S. Pat. No. 5,085,667 issued to Jenkins discloses a procedure for dyeing cationic dyeable nylon with acid or premetalized acid dyes using exhaust/batch dyeing and continuous dyeing techniques, at a pH of from about 4.0 to 6.5. Jenkins discloses a wide variety of acid and premetalized acid dyes as being suitable for dyeing cationic dyeable nylon at a pH of from about 4.0 to 6.5. However, at the pH range of 4.0 to 6.5 disclosed by Jenkins the strike rate is slow. Additionally, many of the acid and premetalized acid dyes listed by Jenkins, such as Nylosan Blue FGBLN (CI No. Acid Blue 127), Intrachrome Black WA (CI No. Acid Black 52) and Telon Black LDN (CI No. Acid Black 172) show poor exhaustion characteristics in medium to full depth shades at the disclosed pH range of 4.0 to 6.5. Consequently, at the pH range of 4.0 to 6.5, an unacceptable amount of unfixed dye remains in the waste water, resulting in the availability of only a light to medium depth of shade and the need to treat the waste water prior to disposal.
Japanese Pat. Application Publication Nos. 1-223908 and 260,061 recognized these problems, teaching that cationic dyeable polyamide fiber dyed with premetalized acid 1:2 acid dyes, at a pH of 7-8, exhibits high dye fastness, while milling acid dyes have weak bonding strength, give low fastness, low dye deposit (exhaustion) and low color intensity. As a result of slow strike rate, bleeding of the dyes occurs and color selection is limited.
Thus, a need exists in the art for a cationic polyamide fiber continuous dyeing, space dyeing or printing process which exhibits improved dye exhaustion and a faster strike rate, which allows for the use of a full spectrum of dye colors, and which results in intense, saturated colors (deep shades).
It has now been found that strike rate and dye exhaustion can be dramatically improved, especially in the medium to dark dye shades, when cationic dyeable polyamide fiber is continuous dyed, space dyed or printed with acid or premetalized acid dyes at a pH of 2.5 and below. At this pH, given the dramatically improved strike rate and exhaustion, a full spectrum of dye colors can be applied to the fiber, with highly contrasting and high intensity color depth, with little or no coloring of the waste water. Moreover, when space dyeing or printing techniques are used, little or no cross staining of the adjoining colored fiber occurs.